Pinpointing apparatus is commonly found in the form of a rotary type pencil sharpener which is well suited to small workpiece sharpening operations. One usual form of such pencil sharpener comprises a pair of cylindrical rollers having a plurality of helical cutting surfaces formed along the longitudinal periphery of each roller. The long axis of each roller is positioned at an angle with respect to a longitudinal sharpening axis about which the rollers both rotate in a manner such that each roller turns about its own axis counter-rotatively with respect to the other roller as both rollers rotate about the sharpening axis. A pencil inserted at a divergent open end of the inclined rollers has a point formed thereon as it is urged towards the converging end of the rollers.
In the case of pinpointing larger objects such as surveying stakes, posts, columns and the like, certain problems can be expected with a pencil sharpening apparatus that is upscaled to accommodate larger workpieces. For example, larger cutting rollers would be substantially more costly to produce than their smaller counterparts used in pencil sharpeners. Moreover, the plurality of helical cutting surfaces would likely require expensive periodic sharpening since sharpening a cutting surface in the form of a helix is a relatively complex procedure that is not easily performed in the field. Furthermore, even a single damaged cutting surface could be beyond repair which would then necessitate replacing the entire roller.
Another form of useful pinpointing apparatus employs a cutting tool holder that may be either conical or cylindrical in form. A plurality of cutting blades are mounted on inner side walls of the tool holder which is rotatably driven. Thus, a workpiece urged coaxially into a rotating conical tool holder will have the inserted end cut into a conical shape as disclosed in U.S. Pat. No. 3,118,476 Fiore.
In the case of the cylindrically shaped cutting tool holder, a workpiece rotatably urged inside the holder against the rotating side wall at an angle will form a point corresponding to the angle of entry as disclosed in U.S. Pat. No. 5,109,896 Tomes et al.
The relatively complex shape of the tool holders in the aforenoted pinpointing apparatus suggests equipment that is costly to both manufacture and maintain.